Whether sensation is in the brain.

One asks further whether sensation is in the brain.

1. It seems that it is. The first in each genus is, according to the Philosopher in the second book of the Metaphysics, exemplary of the genus. Thus, because fire is the first heat, therefore of all things it is especially hot. But the brain is the principle of the sensitive power because the sensitive nerves arise from the brain's web. Therefore, sensation thrives especially in the brain.

2. In addition, touch is the guardian for the entire bodily mechanism, as both the Philosopher and Avicenna say. If, then, touch thrives in any part of the body, then it thrives, as a result, in the brain.

The Philosopher says the opposite. For he says that sensation is not in the brain, and it is not in any other moisture.

To this one must respond that sensation is not in the brain, taken absolutely. The reason for this is that sensation does not occur without heat. The brain, however, is a cold member, for it is composed of earth and water. This is why, when the brain is cooked, it resembles earth, according to Isaac [Israeli] in his On Diets [Dietae]. And this is why the brain cannot be the instrument of sensation.

Furthermore, sensation does not occur without blood or something analogous to blood, as is said in the text. But there is no blood in the brain, and therefore neither is there sensation. Notwithstanding the fact that there is no sensation in blood, according to the Philosopher, nevertheless without blood or something analogous to it there is no sensation. This is because something generated from blood or served by the blood is the first instrument of sensation. It is the same for the brain, because certain things are generated from the brain's power for example, the animal spiritswithout which there could be no sensation. Now, the vital spirits are generated in the heart and flow through the arteries to the brain, and there, owing to the brain's coldness and the narrowness of the veins and the opposition to their motion, these become animal spirits. And then they are sent to the particular senses, and this is why the animal spirits immediately proceed from the brain only to three senses: namely, hearing, smell, and sight. For this reason, it is said that the brain is the principle of the senses, although in a formal sense sensation is not in it.

1. To the arguments. To the first argument, that that which is first in a genus is exemplary of that genus, it must be said that this is true of those that share the same name and cause, but not of other things. For although the sun is the principle of heat, nevertheless it is not exemplary of the genus in act because there is no elemental quality in the sun.

Or, it can be stated otherwise that just as the sun is the principle of heat and nevertheless is not, formally, the first hot principle, thus too it can be said that even though the brain is the principle of sensation, nevertheless it is not the first sentient.

2. To the second argument one should respond that touch is the guardian of the whole bodily machine, but nevertheless it is not present organically in every part of the body. Rather, there are certain parts in which touch does not exist, and this is why these parts are surrounded by other parts, in which touch is present. Such parts are the humors, and this is why, etc.

Whether the vital power has something analogous to it and whether it exists in some organ.

It is asked further whether the vital power has something analogous to it and whether it exists in some organ.

1. It seems not. A universal power corresponding to the entire body does not have a part as an organ. This is evident from the power of growth [virtus augmentativa], because every part grows. This is why life is not in an organ, but rather every part participates in life. This is why it is not in a part as if in an organ.

2. In addition, organs depend on their functions, and the functions proceed from the powers. An organ does not correspond to that act that proceeds immediately from substance but only to that which proceeds from a power. But life proceeds from substance or immediately from the soul. Therefore, life is not in some part as if in an organ.

On the contrary. Every organic operation proceeds through some mediating bodily part. But in these lower regions life is a bodily operation. For we live in the soul and the body, as is said in the second book of On the Soul. Therefore, it occurs through some mediating part.

It must be said that life is present in a given part as if in an organ, because the soul is one and the parts of the body are many. Since, then, it is necessary for there to be some order among the parts in one thing having several parts (otherwise, there would be no unity there), it is necessary that there be one part of the body on which other parts depend. And it is necessary that the first seat of the soul be in this part, and from this part the powers of the soul must flow to the other parts. This part is the heart, because the heart is the first one generated in the animal, and the first to live and the last to die, which would not be so if life were not based in the heart; and this is why the heart is situated in the middle [of the body] just as the prince is in the middle of his kingdom. Thus perhaps one can say that the soul is not in every part, just as the prince is not in every part of the kingdom, but rather dwells more in a castle or in the middle of the kingdom.

1. On to the arguments. To the first argument one must respond that life is in every part of the body, but it is in the heart in a radical way and in other parts by virtue of participation and power, just as a king living in the middle of the realm lives in all parts of the realm in power and by virtue of participation. And this is why the heart is the proper organ of life.

2. To the second argument one must reply that although the soul is the first principle of life, nevertheless it is not the immediate principle, because life does not extend from the soul except through some mediating power, like the sensitive or vegetative power, since sensation is a sort of life; and this is why, etc.